-) Industar and case
The Industar 50-2 was kind of kit-lens for the Zenit. The same time it is a pancake lens.
I know it was not designed as such, but being initially designed for cameras without mirrorbox and due the resulting long barrel, it was tried to build it most compact for its front barrel, what, being used on a SLR made it a pancake lens.
It being as kit lens so compact, did it not make sense to give that kit a flat everready case? But all Zenit cases I came across have that huge snoot, for much bigger lenses.
-) E- model and strap lugs
The standard situation was that early european SLRs were lacking strap lugs and needed an everready case which then got them. Until at later models the camera got strap lugs itelf.
However the Zenit already started with strap lugs. And got everready cases that got straps itself.
With the E-model the camera lost its own lugs. Why?
To avoid having two sets of straps (camera and case)? A pair of carbine hooks would have solved that...